Hypotheses for the Evolution of Reduced Reactive Aggression in the Context of Human Self-Domestication

Probably not a substantial claim: may not pass S2 (checkable), S4 (based).

Language-based conspiracy is the most convincing mechanism for explaining the selective pressure against individually powerful fighters.

“because it is the most convincing mechanism for explaining the selective pressure against individually powerful fighters.”

May combine two claims.

Facial width and brow-ridge projection have declined in H. sapiens.

“Facial width and brow-ridge projection have also declined in H. sapiens (Cieri et al., 2014).”

• cites Cieri et al., 2014 sourceNot checked yet

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Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

Group-structured culture selection possibly accelerated the process of self-domestication.

“Group-structured culture selection possibly accelerated the process.”

May combine two claims.

The Jebel Irhoud specimens have short faces, small teeth, and reduced brow-ridges compared to pre-sapiens ancestors, making them the earliest human specimens to show features of the domestication syndrome.

“The Jebel Irhoud specimens have short faces, small teeth, and reduced brow-ridges compared to pre-sapiens ancestors, making them the earliest human specimens to show features of the domestication syndrome.”

• cites Hublin et al., 2017 sourceNot checked yet

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May combine two claims.

Selection has acted to reduce the propensity for reactive aggression in bonobos compared to a chimpanzee-like ancestor, such that male bonobos who use reactive aggression to achieve an alpha position by being the most effective fighter would not tend to achieve maximal fitness.

“In other words selection has acted to reduce the propensity for reactive aggression in bonobos, compared to a chimpanzee-like ancestor, such that male bonobos who use reactive aggression to achieve an alpha position by being the most effective fighter would not tend to achieve maximal fitness.”

• AssumptionThe authors state this as an assumption: The ancestral Homo species sometimes called Homo heidelbergensis lived in social communities and had dominance hierarchies typical of primates living in multi-female, multi-male groups.
• AssumptionThe authors state this as an assumption: In the ancestral Homo species, there was an alpha male who achieved his position by physically defeating lower-ranking males in one-on-one combat.
• AssumptionThe authors state this as an assumption: The alpha male dominated all females and experienced higher fitness than other males.

Classified as probably not a substantial claim.

Features of the domestication syndrome were produced by selection purely for docility, i.e., for a low propensity for reactive aggression.

“Belyaev (1969) showed that features of the domestication syndrome were produced by selection purely for docility, i.e., for a low propensity for reactive aggression (Trut, 1999).”

• cites Belyaev, 1969Not checked yet

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• cites Trut, 1999 sourceNot checked yet

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Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

Marean (2015) developed a version of the group selection hypothesis suggesting why selection in favor of cooperation was more intense in the origin of H. sapiens than in other Homo, pointing to increasing exploitation of dense and predictable food resources, leading to higher population density, and more aggressive defense of territories.

“Marean (2015) developed a version of this hypothesis that suggested why selection in favor of cooperation was more intense in the origin of H. sapiens than in other Homo. He pointed to increasing exploitation of dense and predictable food resources, leading to higher population density, and more aggressive defense of territories.”

• cites Marean, 2015 sourceNot checked yet

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Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based). May combine two claims.

The explanation for selection against reactive aggression must apply only to H. sapiens, since it is the only species of Homo known to exhibit a domestication syndrome.

“The second challenge is that the explanation for selection against reactive aggression must apply only to H. sapiens, since it is the only species of Homo known to exhibit a domestication syndrome.”

Classified as probably not a substantial claim.

If the male-coalition suppression mechanism applied throughout the existence of H. sapiens, it would explain how there was selection against the best individual fighters.

“If this mechanism applied throughout the existence of H. sapiens, it would explain how there was selection against the best individual fighters [see (8) and (9) below].”

• AssumptionThe authors state this as an assumption: The present informs the past.
• AssumptionRests on an assumption: Contemporary mobile hunter-gatherer societies offer a guide to reconstructing late Pleistocene societies.

May combine two claims.

Living adult males with relatively narrower faces tend both to be less reactively aggressive and to be perceived as being less aggressive, to the point of being assessed as having more human-like minds.

“In support of the behavioral significance of recent anatomical changes, living adult males with relatively narrower faces tend both to be less reactively aggressive and to be perceived as being less aggressive (Carré and McCormick, 2008; Haselhuhn et al., 2015), to the point of being assessed as having more human-like minds (Deska et al., 2018).”

• cites Carré and McCormick, 2008Not checked yet

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• cites Haselhuhn et al., 2015 sourceNot checked yet

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• cites Deska et al., 2018 sourceNot checked yet

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Classified as probably not a substantial claim.

The high degree of docility characteristic of humans and domesticated animals depends on a low propensity for reactive aggression.

“The high degree of docility that is characteristic of humans and domesticated animals depends on a low propensity for reactive aggression, but what relationship it has with proactive aggression, if any, is unknown (Wrangham, 2018).”

• cites Wrangham, 2018 sourceNot checked yet

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Probably not a substantial claim: may not pass S4 (based).

There is reason to question the core assumption that success in intergroup conflict is increased by a reduction in within-group conflict.

“Finally, there is reason to question the core assumption that success in intergroup conflict is increased by a reduction in within-group conflict.”

May combine two claims.

In recent cases GSCS has little relevance for genetic evolution of populations, and none for genetic evolution of the species as a whole.

“In those cases it has little relevance for genetic evolution of populations, and none for genetic evolution of the species as a whole.”

Classified as probably not a substantial claim.

Hypotheses for the evolution of increased cooperation could in theory contribute to explaining why docility evolved.

“Hypotheses for the evolution of increased cooperation could therefore in theory contribute to explaining why docility evolved (e.g., Henrich, 2016; Richerson et al., 2016).”

• cites Henrich, 2016 sourceNot checked yet

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• cites Richerson et al., 2016 sourceNot checked yet

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Probably not a substantial claim: may not pass S4 (based).

Sophisticated language enabled males of low fighting prowess to cooperatively plan the execution of physically aggressive and domineering alpha males.

“Sophisticated language enabled males of low fighting prowess to cooperatively plan the execution of physically aggressive and domineering alpha males.”

Probably not a substantial claim: may not pass S3 (load-bearing).

The earliest record of a lineage of H. sapiens comes from around 315,000 years ago from Jebel Irhoud, Morocco.

“Currently the earliest record of a lineage of H. sapiens comes from around 315,000 years ago from Jebel Irhoud, Morocco (Hublin et al., 2017).”

• cites Hublin et al., 2017 sourceNot checked yet

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May combine two claims.

In bonobos, the alpha male ordinarily owes his position to the support of his mother rather than to his ability to fight alone, and he is not necessarily dominant to the alpha female.

“In bonobos, there is an alpha male, but he ordinarily owes his position to the support of his mother rather than to his ability to fight alone, and he is not necessarily dominant to the alpha female (Surbeck et al., 2011).”

• cites Surbeck et al., 2011 sourceNot checked yet

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May combine two claims.

In some human societies a coalition of the majority prevents any individuals from dominating access to preferred resources, and there are no alpha males (reverse dominance hierarchy).

“In some societies a coalition of the majority is able to prevent any individuals from dominating access to preferred resources (Boehm, 1999). In these cases, called a “reverse dominancy hierarchy” or “counter-hierarchy” there are no alpha males (Boehm, 1993).”

• cites Boehm, 1999 sourceNot checked yet

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• cites Boehm, 1993 sourceNot checked yet

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May combine two claims.

The group selection argument does not differentiate between humans and chimpanzees, even though only humans, and not chimpanzees, have experienced selection against reactive aggression.

“The group selection argument thus does not differentiate between humans and chimpanzees, even though only humans, and not chimpanzees, have experienced selection against reactive aggression.”

Classified as probably not a substantial claim. May combine two claims.

Human aggressiveness comes in two major forms, reactive (or impulsive) and proactive (or premeditated), each with their own distinctive neurobiology.

“Human aggressiveness has recently been argued to come in two major forms, reactive (or impulsive) and proactive (or premeditated), each with their own distinctive neurobiology (Wrangham, 2018).”

• cites Wrangham, 2018 sourceNot checked yet

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Probably not a substantial claim: may not pass S3 (load-bearing).

Group selection has been proposed as a mechanism for promoting parochial altruism.

“Group selection has been proposed as a mechanism for promoting parochial altruism, meaning altruism restricted to “one’s own ethnic, racial, or other group” (Choi and Bowles, 2007: 636).”

• cites Choi and Bowles, 2007Not checked yet

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Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based). May combine two claims.

There is no direct evidence as to whether, around the time that H. sapiens evolved, foods could no longer be collected individually, teamwork against predators became much more important, or pair-bonding began.

“For example there is no direct evidence as to whether, around the time that H. sapiens evolved, foods could no longer be collected individually, teamwork against predators became much more important, or pair-bonding began.”

Probably not a substantial claim: may not pass S1 (asserted).

The argument is that cooperative breeding was a feature of the genus Homo from H. erectus onward, close to 2 million years ago.

“First, the argument made by Hrdy (2009), Burkart et al. (2009), and Burkart and van Schaik (2016) is that cooperative breeding was a feature of the genus Homo from H. erectus onward, close to 2 million years ago.”

• cites Hrdy, 2009Not checked yet

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• cites Burkart et al., 2009 sourceNot checked yet

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• cites Burkart and van Schaik, 2016Not checked yet

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Probably not a substantial claim: may not pass S4 (based).

Hypotheses of social selection for unaggressive partners are challenged by the predictable success of a tyrant using brute force for personal gain.

“In short, hypotheses of social selection for unaggressive partners are challenged by the predictable success of a tyrant using brute force for personal gain.”

Probably not a substantial claim: may not pass S3 (load-bearing).

Marean developed a similar scenario.

“Marean (2015) developed a similar scenario.”

• cites Marean, 2015 sourceNot checked yet

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Classified as probably not a substantial claim.

Selection favored a low propensity for male aggression because offspring were thereby better protected from the father's potential violence.

“Selection favored a low propensity for male aggression because offspring were thereby better protected from the father’s potential violence.”

• cites Tomasello, 2016 sourceNot checked yet

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Classified as probably not a substantial claim.

In societies with higher-status women, men were relatively short, suggesting reduced selection for male aggressiveness.

“In support, they found that in societies with higher-status women (who were presumed to have more freedom to choose their mates), men were relatively short (suggesting reduced selection for male aggressiveness).”

• cites Gleeson and Kushnick, 2018Not checked yet

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Probably not a substantial claim: may not pass S1 (asserted), S3 (load-bearing).

Increasing population density around 200,000 years ago could have been responsible for selection pressures against reactive aggression.

“Cieri et al. (2014) proposed that increasing population density around 200,000 years ago could have been responsible for selection pressures against reactive aggression.”

• cites Cieri et al., 2014 sourceNot checked yet

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Probably not a substantial claim: may not pass S4 (based).

If group cultures in the form of social norms occurred as early as 300,000 years ago, GSCS might have contributed to selection against reactive aggression.

“Nevertheless, if group cultures in the form of social norms occurred as early as 300,000 years ago, GSCS might have contributed to selection against reactive aggression.”

Probably not a substantial claim: may not pass S3 (load-bearing).

Increasing population density was plausibly associated with the cultural developments around 300,000 years ago.

“In favor of this general kind of idea, increasing population density was plausibly associated with the cultural developments reported by Brooks et al. (2018) around 300,000 years ago.”

• cites Brooks et al., 2018 sourceNot checked yet

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May combine two claims.

The self-control hypothesis is challenged by the problems of why the sapiens lineage took a different course from other Homo, and by the problem of how increased self-control would lead to selection against domineering behaviors.

“It is challenged by the problems of why the sapiens lineage took a different course from other Homo, and by the problem of how increased self-control would lead to selection against domineering behaviors.”

Probably not a substantial claim: may not pass S1 (asserted). May combine two claims.

Higher population density could have increased the pressure to exploit resources controlled by other humans, and would have selected for increased social tolerance toward unfamiliar individuals, an extension of social networks, and more sharing of acquired foods.

“They suggested that because higher population density could have increased the pressure to exploit resources controlled by other humans, it would have selected for increased social tolerance toward unfamiliar individuals, an extension of social networks, and more sharing of acquired foods.”

• cites Cieri et al., 2014 sourceNot checked yet

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May combine two claims.

Effective cooperation depended on a reduction in selfishness and aggressiveness, and on a concomitant increase in sympathy and shared intentionality.

“Effective cooperation depended on a reduction in selfishness and aggressiveness, and on a concomitant increase in sympathy and shared intentionality.”

• cites Tomasello, 2016 sourceNot checked yet

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Probably not a substantial claim: may not pass S1 (asserted), S2 (checkable), S3 (load-bearing), S4 (based). May combine two claims.

An alternative proposal that could have involved GSCS attributes selection against reactive aggression to the emergence of language-based conspiracy that would allow execution of aggressive individuals.

“An alternative proposal that could have involved GSCS attributes selection against reactive aggression to the emergence of language-based conspiracy that would allow execution of aggressive individuals.”

Probably not a substantial claim: may not pass S1 (asserted).

Self-domestication could be promoted by an increased ability for self-control leading to less use of reactive aggression.

“Based on the latter finding, Hare (2017) suggested that self-domestication could be promoted by an increased ability for self-control leading to less use of reactive aggression.”

• cites Hare, 2017Not checked yet

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Probably not a substantial claim: may not pass S4 (based).

Tomasello does not discuss what would stop a determined, physically powerful male from exerting his fighting ability at the expense of others in his group.

“Similar to the problem with the female mate choice hypothesis, the difficulty is that Tomasello does not discuss what would stop a determined, physically powerful male from exerting his fighting ability at the expense of others in his group.”

Classified as probably not a substantial claim. May combine two claims.

Applying the hypothesis specifically to self-domestication, selected effects could in theory include reduced tendencies for reactive aggression, on the traditional premise that groups in which males competed more aggressively with group members would be less effective at intergroup conflict.

“Applying the hypothesis specifically to the problem of self-domestication, selected effects could in theory include reduced tendencies for reactive aggression, on the traditional premise that groups in which males competed more aggressively with group members would be less effective at intergroup conflict (e.g., Zhang et al., 2019).”

• cites Zhang et al., 2019 sourceNot checked yet

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May combine two claims.

The cooperative breeding proposal has no special claim on events surrounding the evolution of H. sapiens around 300,000 years ago: it does not help explain the evidence that H. sapiens underwent a singular form of self-domestication not experienced by other Homo species.

“Their proposal therefore has no special claim on events surrounding the evolution of H. sapiens around 300,000 years ago: it does not help explain the evidence that H. sapiens underwent a singular form of self-domestication not experienced by other Homo species.”

Probably not a substantial claim: may not pass S3 (load-bearing).

In experimental studies with captive primates, population density is sometimes associated with reduced aggression and increased tolerance.

“In experimental studies with captive primates, population density is sometimes associated with reduced aggression and increased tolerance (Aureli et al., 2000).”

• cites Aureli et al., 2000 sourceNot checked yet

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Probably not a substantial claim: may not pass S2 (checkable).

Such findings mean that a specific theory is needed to explain why intergroup conflict would have led to reactive aggression being selected against more intensely in Homo ∼300,000 years ago than happens in other primates.

“Such findings mean that a specific theory is needed to explain why intergroup conflict would have led to reactive aggression being selected against more intensely in Homo,∼300,000 years ago, than happens in other primates.”

Probably not a substantial claim: may not pass S3 (load-bearing).

Tomasello presented an explanation for the evolution of morality that included a proposal for the reduction of aggressiveness in H. sapiens, called the interdependence hypothesis.

“This general idea has been elaborated particularly clearly by Tomasello (2016), who presented an explanation for the evolution of morality that included a proposal for the reduction of aggressiveness in H. sapiens. Tomasello called it the “interdependence hypothesis.””

• cites Tomasello, 2016 sourceNot checked yet

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Classified as probably not a substantial claim. May combine two claims.

In primates, absolute brain size predicts neuron number and is strongly correlated with the ability to inhibit prepotent responses.

“In primates, absolute brain size predicts neuron number and is strongly correlated with the ability to inhibit prepotent responses (MacLean et al., 2014).”

• cites MacLean et al., 2014 sourceNot checked yet

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Classified as probably not a substantial claim. May combine two claims.

Gene-culture coevolution would then include selection in favor of an increasingly parochial-altruistic psychology: tendencies for docility and conformity would be favored because individuals with those characteristics would readily acquire group norms.

“Gene-culture coevolution would then include selection in favor of an increasingly parochial-altruistic psychology: tendencies for docility and conformity would be favored because individuals with those characteristics would readily acquire group norms (Richerson et al., 2016).”

• cites Richerson et al., 2016 sourceNot checked yet

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Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

Female choice of less aggressive males as mates was proposed as a mechanism that could promote self-domestication, because females who choose less aggressive males can benefit by their mates' greater investment in shared parenting effort.

“Female choice of less aggressive males as mates was proposed by Cieri et al. (2014) and Gleeson and Kushnick (2018) as a mechanism that could promote self-domestication, because females who choose less aggressive males can benefit by their mates’ greater investment in shared parenting effort.”

• cites Cieri et al., 2014 sourceNot checked yet

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• cites Gleeson and Kushnick, 2018Not checked yet

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Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

Island populations of rodents, lizards and birds tend to live at higher density than their continental relatives and also show low levels of aggression.

“Island populations tend to live at higher density than their continental relatives, and also to show low levels of aggression (Stamps and Buechner, 1985).”

• cites Stamps and Buechner, 1985Not checked yet

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Probably not a substantial claim: may not pass S3 (load-bearing).

According to the interdependence hypothesis, the initial influence on the road to a human style of morality occurred around 400,000 years ago when there was a disappearance of individually obtainable foods.

“According to the interdependence hypothesis the initial influence on the road to a human style of morality occurred around 400,000 years ago when there was a “disappearance of individually obtainable foods” (Tomasello, 2016: 136).”

• cites Tomasello, 2016 sourceNot checked yet

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Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

Like a male lion feeding off the kills brought down by females, the determinedly aggressive and effective fighter would continue to have high fitness thanks to his ability to commandeer food, mates or other resources from others in the group.

“Like a male lion Panthera leo feeding off the kills brought down by females, the determinedly aggressive and effective fighter would continue to have high fitness thanks to his ability to commandeer food, mates or other resources from others in the group.”

Probably not a substantial claim: may not pass S4 (based). May combine two claims.

The despotic male would improve his lot by seizing the choicest foods that others produced: his physical dominance would allow it.

“The despotic male would improve his lot by seizing the choicest foods that others produced: his physical dominance would allow it.”

Probably not a substantial claim: may not pass S4 (based).

The only obvious solution would be that the tyrant is constrained by coalitions that can physically rein in his power.

“The only obvious solution would be that the tyrant is constrained by coalitions that can physically rein in his power, similar to the solution for social selection by female mate choice.”

Classified as probably not a substantial claim.

The tribal social instincts hypothesis suggests that groups in which there were norms of parochial altruism would have been especially successful in intergroup competition.

“This hypothesis suggests that groups in which there were norms of parochial altruism would have been especially successful in intergroup competition.”

• cites Richerson and Boyd, 1998Not checked yet

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Probably not a substantial claim: may not pass S4 (based).

Increased social tolerance implies a reduced propensity for reactive aggression.

“Increased social tolerance implies a reduced propensity for reactive aggression.”

Probably not a substantial claim: may not pass S2 (checkable), S3 (load-bearing).

The notion of a relevant ecological change is entirely speculative.

“Thus the notion of a relevant ecological change is entirely speculative.”

May combine two claims.

Effective population size of H. sapiens fell from 200,000 years ago to 50,000-30,000 years ago, suggesting a mismatch between cultural development and population density.

“On the other hand, genetic data indicate that effective population size of H. sapiens fell from 200,000 years ago to 50,000–30,000 years ago, suggesting a mismatch between cultural development and population density (Steele and Weaver, 2014).”

• cites Steele and Weaver, 2014Not checked yet

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Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based). May combine two claims.

While such selection is theoretically possible, no cases have yet been documented of GSCS leading to genetic change.

“While such selection is theoretically possible, to my knowledge no cases have yet been documented of GSCS leading to genetic change.”

Classified as probably not a substantial claim. May combine two claims.

Cooperative breeding became an important feature of early Homo society and selected for increased social tolerance.

“Burkart et al. (2009), Hrdy (2009), and Burkart and van Schaik (2016) proposed that cooperative breeding, a social system in which individuals help rear others’ offspring at a cost to their own reproductive effort, became an important feature of early Homo society and selected for increased social tolerance.”

• cites Burkart et al., 2009 sourceNot checked yet

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• cites Hrdy, 2009Not checked yet

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• cites Burkart and van Schaik, 2016Not checked yet

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May combine two claims.

Coalitionary support is needed to enable partner choice to be effective, but coalitionary support has not featured to date in the social selection hypotheses.

“Coalitionary support is needed to enable partner choice to be effective, but coalitionary support has not featured to date in the social selection hypotheses.”

May combine two claims.

Language-based conspiracy appears to be a vital prerequisite for controlling a would-be despot in a mobile hunter-gatherer society, and seems likely to have been equally important in the past.

“For those reasons, language-based conspiracy appears to be a vital prerequisite for controlling a would-be despot in a mobile hunter-gatherer society, and seems likely to have been equally important in the past.”

May combine two claims.

In humans, groups conspire against resented tyrants; in mobile hunter-gatherers plans are made and tyrants are executed.

“In humans, by contrast, groups conspire against resented tyrants: in mobile hunter-gatherers plans are made and tyrants are executed.”

Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

Lethal weaponry would have facilitated executions.

“Lethal weaponry would also have facilitated executions.”

May combine two claims.

Experimental studies of captive primates show that high population density can lead to an increase in the rate of aggression, or can have no effect.

“and experimental studies of captive primates show that high population density can lead to an increase in the rate of aggression, or can have no effect (Cordoni and Palagi, 2007; Crast et al., 2015).”

• cites Cordoni and Palagi, 2007Not checked yet

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• cites Crast et al., 2015 sourceNot checked yet

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Probably not a substantial claim: may not pass S3 (load-bearing).

The lethal weapons hypothesis has the merit of suggesting that the use of lethal weapons would lead to selection against reactive aggression.

“Since alpha-males would have maintained their position by reacting violently to challengers, this hypothesis has the merit of suggesting that the use of lethal weapons would lead to selection against reactive aggression.”

Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

The time when language became sufficiently sophisticated that subordinate males could confidently plan to kill a better fighter is speculative.

“As for language-based conspiracy (9), the time when language became sufficiently sophisticated that subordinate males could confidently plan to kill a better fighter is speculative.”

May combine two claims.

In groups that have egalitarian male dominance hierarchies, individual choice of unaggressive mates and unaggressive task partners are plausible influences on the reduction of reactive aggression.

“In groups that have egalitarian male dominance hierarchies both ideas are plausible influences on the reduction of reactive aggression.”

Probably not a substantial claim: may not pass S3 (load-bearing).

Oldowan stone manuports were possibly lethal throwing weapons in the Lower Pleistocene.

“Oldowan stone manuports were possibly lethal throwing weapons in the Lower Pleistocene (Gintis et al., 2015).”

• cites Gintis et al., 2015 sourceNot checked yet

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May combine two claims.

The evolution of this newly sophisticated cognitive ability would have led subordinates to socially select against aggressive fighters, creating a reverse dominance hierarchy.

“The evolution of this newly sophisticated cognitive ability would have led subordinates to socially select against aggressive fighters, creating a reverse dominance hierarchy.”

May combine two claims.

Across species, the precise composition of domestication syndromes is unpredictable, undermining confidence in using them to infer selection against reactive aggression; and the biological mechanisms responsible for producing domestication syndromes are uncertain.

“Against this idea, across species the precise composition of domestication syndromes is unpredictable, a fact that undermines confidence in using them to infer selection against reactive aggression; and the biological mechanisms responsible for producing domestication syndromes are uncertain (Sánchez-Villagra et al., 2016; Sánchez-Villagra and van Schaik, 2019).”

• cites Sánchez-Villagra et al., 2016 sourceNot checked yet

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• cites Sánchez-Villagra and van Schaik, 2019 sourceNot checked yet

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May combine two claims.

Language-based conspiracy is not present in chimpanzees: subordinate chimpanzees cannot plan premeditated take-downs of alpha males, which probably partly explains why there has apparently been no selection against reactive aggression in this species.

“Language-based conspiracy is not present in chimpanzees: subordinate chimpanzees cannot plan premeditated take-downs of alpha males, which probably partly explains why there has apparently been no selection against reactive aggression in this species.”

May combine two claims.

Once reactive aggression started to be selected against, expected effects would have included, as a by-product, increased social tolerance and improved abilities to communicate and cooperate.

“Once reactive aggression started to be selected against, expected effects would have included, as a by-product, increased social tolerance and improved abilities to communicate and cooperate (Hare, 2017).”

• cites Hare, 2017Not checked yet

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Classified as probably not a substantial claim.

Sufficient execution of Pleistocene despots would have led to selection against reactive aggression.

“Sufficient execution of Pleistocene despots would have led to selection against reactive aggression (Wrangham, 2018, 2019).”

• cites Wrangham, 2018, 2019Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

May combine two claims.

Executions can be planned using proactive aggression, so executioners arrange to kill a victim in a circumstance in which fighting back is essentially impossible, and killers incur very low costs.

“An important feature of executions is that they can be planned using proactive aggression. This means that the executioners arrange to kill a victim in a circumstance in which fighting back is essentially impossible. As a result, the killers incur very low costs.”

May combine two claims.

The language-based conspiracy hypothesis can explain why reactive aggression would have been selected against, why this occurred only in H. sapiens, and why reactive aggression has continued to decline.

“In sum, the language-based conspiracy hypothesis can explain why reactive aggression would have been selected against, why this occurred only in H. sapiens, and (given that capital punishment was recorded into contemporary times among mobile hunter-gatherers) why reactive aggression has continued to decline.”

Probably not a substantial claim: may not pass S4 (based).

With weapon use already in place, capital punishment would have been relatively easy.

“With weapon use already in place, capital punishment would have been relatively easy.”

May combine two claims.

No other selective pressures are known to produce a domestication syndrome, and the resemblances that humans show to domesticated animals include physiological, behavioral and cognitive traits in addition to reduced aggression and a derived anatomy.

“Nevertheless, no other selective pressures are known to produce a domestication syndrome, and the resemblances that humans show to domesticated animals include physiological, behavioral and cognitive traits in addition to reduced aggression and a derived anatomy (Hare, 2017; Wrangham, 2019).”

• cites Hare, 2017Not checked yet

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• cites Wrangham, 2019Not checked yet

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Classified as probably not a substantial claim.

The population density hypothesis fails to detail any process responsible for selection directly against alpha-male-style behavior.

“The population density hypothesis also fails to detail any process responsible for selection directly against alpha-male-style behavior.”

May combine two claims.

Current evidence about the evolutionary history of human population density undermines any easy correlations, and the relationship between population density and rates of aggression in primates is inconsistent.

“Current evidence about the evolutionary history of human population density, however, undermines any easy correlations, and the relationship between population density and rates of aggression in primates is inconsistent.”

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

The cooperative breeding hypothesis could in theory account for reduced aggressiveness, although the evidence for cooperative breeders being unaggressive is inconsistent at best.

“The cooperative breeding hypothesis for human social evolution (6) could in theory account for reduced aggressiveness, although the evidence for cooperative breeders being unaggressive is inconsistent at best.”

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

Increasing population density is associated with reduced aggressiveness in island species, and could in theory play a role in H. sapiens' self-domestication.

“Increasing population density (7) is associated with reduced aggressiveness in island species, and could in theory play a role in H. sapiens’ self-domestication.”

Probably not a substantial claim: may not pass S2 (checkable). May combine two claims.

The spread of the new style of hierarchy could have occurred by individual learning or by selection of group-cultures, and would have paved the way for diverse selection pressures to additionally influence the evolution of characteristically human social traits.

“The spread of the new style of hierarchy could have occurred by individual learning or by selection of group-cultures, and would have paved the way for diverse selection pressures, as shown in Table 1, to additionally influence the evolution of the characteristically human social traits.”

May combine two claims.

A biological hypothesis for the production of domestication syndromes has received important support, including evidence that genetic variants underlying self-domestication occur in H. sapiens but not in H. neanderthalensis or Denisovans.

“Furthermore a biological hypothesis for the production of domestication syndromes (Wilkins et al., 2014) has received important support (Wilkins, 2017; Pendleton et al., 2018), including evidence that genetic variants underlying self-domestication occur in H. sapiens but not in H. neanderthalensis or Denisovans (Theofanopoulou et al., 2017).”

• cites Wilkins et al., 2014 sourceNot checked yet

  Not checked in the free run.

• cites Wilkins, 2017 sourceNot checked yet

  Not checked in the free run.

• cites Theofanopoulou et al., 2017 sourceNot checked yet

  Not checked in the free run.

May combine two claims.

Capital punishment has been recorded among mobile hunter-gatherers in every continent, and aggressive bullies are a common type of victim.

“This scenario is supported by the fact that capital punishment has been recorded among mobile hunter-gatherers in every continent, and that aggressive bullies are a common type of victim (Boehm, 2012).”

• cites Boehm, 2012Not checked yet

  Not checked in the free run.

May combine two claims.

Lethal weaponry does not appear to be associated with H. sapiens as tightly or as uniquely as theory would demand, since it has likely been used for a long time before the evolution of H. sapiens, as well as in other species of Homo.

“However, it does not appear to be associated with H. sapiens as tightly or as uniquely as theory would demand, since it has likely been used for a long time before the evolution of H. sapiens, as well as in other species of Homo.”

Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based). May combine two claims.

The use of lethal weapons was probably widespread from H. erectus onward, and would have facilitated the deliberate killing of conspecifics.

“In sum, the use of lethal weapons was probably widespread from H. erectus onward, and would have facilitated the deliberate killing of conspecifics.”

May combine two claims.

Genetic group selection and group-structured culture selection do not account for reduced reactive aggression in H. sapiens in their current form, partly because in humans and other primates effective intergroup conflict is not necessarily associated with reduced within-group aggression.

“I concluded that they do not do so in their current form, partly because in humans, and other primates, effective intergroup conflict is not necessarily associated with reduced within-group aggression.”

Probably not a substantial claim: may not pass S1 (asserted).

Linguistic ability was significantly more sophisticated in H. sapiens than in H. neanderthalensis or other Homo species.

“The prediction made by this hypothesis is that linguistic ability was significantly more sophisticated in H. sapiens than in H. neanderthalensis or other Homo species. That idea is plausible (Tattersall, 2016), though hotly debated (Dediu and Levinson, 2013).”

• cites Tattersall, 2016 sourceNot checked yet

  Not checked in the free run.

• cites Dediu and Levinson, 2013Not checked yet

  Not checked in the free run.

May combine two claims.

Because proactive and reactive aggression involve different neurobiological mechanisms, under a selective regime of alpha males being executed, the propensity for proactive reaction can remain high while the propensity for reactive aggression declines over evolutionary time.

“The fact that proactive and reactive aggression involve different neurobiological mechanisms means that under a selective regime of alpha males being executed, the propensity for proactive reaction can remain high while the propensity for reactive aggression declines over evolutionary time (Wrangham, 2018).”

• cites Wrangham, 2018 sourceNot checked yet

  Not checked in the free run.

Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based). May combine two claims.

The ethnographic record of capital punishment is thin; the practice has tended to disappear very rapidly.

“Unfortunately, however, the ethnographic record of capital punishment is thin: the practice has tended to disappear very rapidly.”

Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

Lethal weaponry has undoubtedly played an important role in human life.

“Lethal weaponry (8) has undoubtedly played an important role in human life.”

May combine two claims.

The group selection argument for parochial altruism does not explain behavioral differences between humans and chimpanzees; and the culture selection argument for tribal social instincts is challenged by the origin of H. sapiens being so early that the requisite cultural abilities may not have been present.

“The group selection argument for parochial altruism also does not explain behavioral differences between humans and chimpanzees; and the culture selection argument for tribal social instincts is challenged by the origin of H. sapiens being so early that the requisite cultural abilities may not have been present.”

May combine two claims.

Chimpanzees cannot communicate to others that they wish to kill a particular individual, nor justify their desire, find out if their partner feels the same way, or plan to meet at a future time and place to carry out the deed.

“Chimpanzees cannot communicate to others that they wish to kill a particular individual, let alone justify their desire, find out if their partner feels the same way, or plan to meet at some future time at a specified place in order to carry out the deed.”